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#include <dart/All.hpp>

#include <gtest/gtest.h>

using dart::dynamics::BodyNode;
using dart::dynamics::Inertia;
using dart::dynamics::Skeleton;
using dart::dynamics::SkeletonPtr;
using dart::dynamics::TranslationalJoint;

// Regression test for https://github.com/dartsim/dart/issues/1681.
TEST(BodyNodePotentialEnergy, UsesCenterOfMass)
{
  SkeletonPtr skeleton = Skeleton::create("skeleton");

  TranslationalJoint::Properties jointProps;
  jointProps.mName = "root_joint";
  BodyNode::Properties bodyProps;
  bodyProps.mName = "body";

  auto pair
      = skeleton->createJointAndBodyNodePair<TranslationalJoint, BodyNode>(
          nullptr, jointProps, bodyProps);
  auto* joint = pair.first;
  auto* body = pair.second;

  Inertia inertia;
  inertia.setMass(2.0);
  inertia.setLocalCOM(Eigen::Vector3d(0.0, 1.0, 0.0));
  inertia.setMoment(Eigen::Matrix3d::Identity());
  body->setInertia(inertia);

  // Place the body so the frame origin and COM differ along gravity.
  joint->setPositions(Eigen::Vector3d(0.3, 0.5, -0.2));

  const Eigen::Vector3d gravity(0.0, -9.81, 0.0);

  const double expected = -body->getMass() * body->getCOM().dot(gravity);
  const double energy = body->computePotentialEnergy(gravity);

  EXPECT_DOUBLE_EQ(energy, expected);
}
